﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

namespace ReflectionStudio.Diagram.Manager.Core.Reflection
{
	class AssemblyTester
	{
		/// <summary>
		/// Return true if the file specified is a real CLR type, otherwise false is returned.
		/// False is also returned in the case of an exception being caught
		/// </summary>
		/// <param name="file">A string representing the file to check for CLR validity</param>
		/// <returns>True if the file specified is a real CLR type, otherwise false is returned.
		/// False is also returned in the case of an exception being caught</returns>
		public bool isDotNetAssembly(String file)
		{
			uint peHeader;
			uint peHeaderSignature;
			ushort machine;
			ushort sections;
			uint timestamp;
			uint pSymbolTable;
			uint noOfSymbol;
			ushort optionalHeaderSize;
			ushort characteristics;
			ushort dataDictionaryStart;
			uint[] dataDictionaryRVA = new uint[16];
			uint[] dataDictionarySize = new uint[16];

			//get the input stream
			Stream fs = new FileStream(@file, FileMode.Open, FileAccess.Read);

			try
			{

				BinaryReader reader = new BinaryReader(fs);
				//PE Header starts @ 0x3C (60). Its a 4 byte header.
				fs.Position = 0x3C;
				peHeader = reader.ReadUInt32();
				//Moving to PE Header start location...
				fs.Position = peHeader;
				peHeaderSignature = reader.ReadUInt32();
				//We can also show all these value, but we will be       
				//limiting to the CLI header test.
				machine = reader.ReadUInt16();
				sections = reader.ReadUInt16();
				timestamp = reader.ReadUInt32();
				pSymbolTable = reader.ReadUInt32();
				noOfSymbol = reader.ReadUInt32();
				optionalHeaderSize = reader.ReadUInt16();
				characteristics = reader.ReadUInt16();
				/*
				  Now we are at the end of the PE Header and from here, the
				  PE Optional Headers starts...
				  To go directly to the datadictionary, we'll increase the      
				  stream’s current position to with 96 (0x60). 96 because,
				  28 for Standard fields
				  68 for NT-specific fields
				  From here DataDictionary starts...and its of total 128 bytes. DataDictionay has 16 directories in total,
				  doing simple maths 128/16 = 8.
				  So each directory is of 8 bytes.
             
				  In this 8 bytes, 4 bytes is of RVA and 4 bytes of Size.
				  btw, the 15th directory consist of CLR header! if its 0, its not a CLR file :)

				  */
				dataDictionaryStart = Convert.ToUInt16(Convert.ToUInt16(fs.Position) + 0x60);
				fs.Position = dataDictionaryStart;
				for (int i = 0; i < 15; i++)
				{
					dataDictionaryRVA[i] = reader.ReadUInt32();
					dataDictionarySize[i] = reader.ReadUInt32();
				}
				if (dataDictionaryRVA[14] == 0)
				{
					fs.Close();
					return false;
				}
				else
				{
					fs.Close();
					return true;
				}
			}
			catch (Exception)
			{
				return false;
			}
			finally
			{
				fs.Close();
			}
		}
	}
}
